摘要
以纤维类型及其体积分数为变量,通过单轴拉伸试验,研究了海砂工程水泥基复合材料(SECC)的单轴拉伸性能,并基于现有工程水泥基复合材料(ECC)的拉伸本构模型,阐述了SECC的稳态开裂机理,提出以强化段与软化段描述SECC拉伸应力-应变关系的波动上升段和下降段,得到了新的适用于SECC的拉伸本构模型.结果表明:纤维体积分数为1.5%的聚乙烯(PE)纤维/SECC表现出饱和多缝开裂的应变硬化行为,其延性可达到3.99%;提出的SECC拉伸本构模型计算结果可准确描述具有稳态开裂行为SECC的拉伸应力-应变关系.
工程水泥基复合材料(ECC)是一种耐磨性、抗剥落性能、耐久性能、自愈合性能和微裂缝控制能力等各项性能良好的纤维增强水泥基复合材
单轴拉伸应力-应变关系可反映ECC各个受力阶段的破坏过程和变形特点,是ECC最基本的本构关系,也是研究其结构承载力和变形的重要依
本研究团队制备了海砂工程水泥基复合材料(SECC
水泥为海螺牌P·O 42.5水泥;辅助胶凝材料为河南某火电厂提供的Ⅰ级粉煤灰、偏高岭土、硅砂,粉煤灰的中位粒径为13.0 μm,需水量比(质量比,文中涉及的组成、比值等除特殊说明外均为质量分数或质量比)0.92,偏高岭土的中位粒径为6.5 μm,硅砂的中位粒径为68.0 μm.水泥、粉煤灰和偏高岭土的化学组成见

图1 粉煤灰、偏高岭土和硅砂的粒度曲线
Fig.1 Particle size distributions of fly ash, metakaolin and silica sand
PVA纤维为日本生产的REC‑15,PE、PVA纤维的物理和力学性能见
用单轴拉伸试验测试SECC的应变能力,试件为矩形薄板试样,其尺寸为400 mm×100 mm×15 mm.为使夹具更好地夹紧试件,并避免夹持部分产生应力集中,在试件两端采用环氧树脂胶粘贴1层碳纤维增强复合材料(CFRP)布及铝板(CFRP布可提高试件与铝板间的黏结),单轴拉伸试验试件示意图见

图2 单轴拉伸试验试件示意图
Fig.2 Schematic diagram of uniaxial tensile test specimens (size: mm)
SECC的拉伸应力σ-应变ε曲线见

图3 SECC的拉伸应力-应变曲线
Fig.3 Tensile stress‑strain curves of SECC
对于PVA/SECC:PVA/SECC的极限拉伸应力、极限拉伸应变均随PVA纤维体积分数的降低而降低,这是由于PVA/SECC的流动度随纤维体积分数的增加而降低(见

图4 SECC破坏形式
Fig.4 Failure modes SECC
SECC拉伸断面的SEM图见

图5 SECC拉伸断面的SEM图
Fig.5 SEM images of tensile section of PE/SECC specimens
对于PE/SECC:2PE/SECC和1PE/SECC的抗拉强度、延性十分接近,极限拉伸应变仅相差0.10%;1.5PE/SECC表现出了饱和多裂缝开展的应变硬化行为(
由
以往的研

图6 ECC的双线模型及其在1.5PE/SECC中的应用
Fig.6 Bilinear models of ECC and its application in 1.5PE/SECC
基于上述原因,本文提出了新的SECC拉伸本构模型:
(1) |
式中:εcr、εp分别为初裂应变、极限拉伸应力对应的应变;k为强化系数,;α为衰减系数.
进行单轴拉伸试验时,由于安装夹具及试验机夹头夹紧夹具时可能会造成试件中心轴线偏离加载方向,导致初始偏心,造成实测初裂荷载值偏低.因此,本文将线弹性阶段与应变硬化阶段中的强化段拟合所得直线的交点定义为名义初裂
因试件到达软化阶段时已完全失去承载力,故在SECC的拉伸本构模型中将其忽略.根据L
本文SECC的裂纹桥接应力σc达到峰值后并未像传统的ECC软化后下降,而是波动下降,即仍能产生裂纹并具有一定的承载力.这是由于荷载达到峰值时,主裂纹仍未贯穿试件横截面,导致其仍能承担拉伸荷载,并具有稳态开裂行为,与峰前拉伸应力-应变关系不同的是,峰后拉伸应力-应变曲线是波动下降的.这可能是由于荷载达到峰值后,试件多处纤维发生拔出破坏,纤维/基体间的摩擦黏结强度τ下降,导致复合材料的裂纹桥接应力σc下降.
将SECC拉伸应力-应变关系曲线中的应变硬化阶段分为强化段与软化段,强化段为初裂应力至极限拉伸应力对应的曲线, 软化段为极限拉伸应力对应的应变至极限拉伸应变对应的曲线,并将其简化为线性关系,结果见
Hardening stage: | (2) |
Softening stage: | (3) |
(4) |

图7 SECC受拉应力-应变曲线简化模型
Fig.7 Simplified tensile stress‑strain curve of SECC
采用最小二乘法对具有应变硬化行为试件的试验数据进行回归分析,得到k、α,结果见
为验证本文提出的SECC拉伸本构模型,将模拟拉伸应力-应变曲线与试验曲线进行对比,结果见

图8 SECC拉伸本构模型模拟结果与试验曲线对比
Fig.8 Comparison between modified results from tensile constitutive model and test curves of SECC
由于2PVA/SECC和2PE/SECC的初裂点与极限拉伸应力对应的点十分接近,2PE/SECC‑2的初裂点甚至与极限拉伸应力点重合(见
(1)聚乙烯醇(PVA)纤维、聚乙烯(PE)纤维海砂工程水泥复合材料(PVA/SECC、PE/SECC)的最优纤维体积分数分别为2.0%、1.5%.纤维体积分数为1.5%的PE/SECC表现出饱和多缝开裂的应变硬化行为,延性可达到3.99%,与2PE/SECC和1PE/SECC相比提高约487.00%.
(2)PVA/SECC与PE/SECC的流动度均随纤维体积分数的增加而降低,PVA/SECC的流动度比PE/SECC的流动度高12.4%~25.9%;纤维体积分数为1.5%的PE/SECC流动度与PVA/SECC的流动度最接近.
(3)本文提出将SECC应变硬化阶段分为强化段与软化段,以解决传统ECC双线模型在SECC中应用所造成的承载力过剩问题.建立的SECC拉伸本构模型与试验结果基本吻合,但该模型不适用于无稳态开裂行为的SECC.
参考文献
李庆华, 徐世烺. 超高韧性水泥基复合材料基本性能和结构应用研究进展[J]. 工程力学, 2009(增刊2):23‑67. [百度学术]
LI Qinghua, XU Shilang. Performance and application of ultra high toughness cementitious composite:A review [J]. Engineering Mechanics, 2009(Suppl 2):23‑67. (in Chinese) [百度学术]
李祚, 姚淇耀, 朱圣焱, 等.乌兰布和沙漠砂制备高延性水泥基复合材料的力学性能[J]. 硅酸盐通报, 2021, 40(4):1103‑1115. [百度学术]
LI Zuo, YAO Qiyao, ZHU Shengyan, et al. Mechanical properties of engineered cementitious composites prepared with sand in Ulanbuh desert [J]. Bulletin of the Chinese Ceramic Society, 2021, 40(4):1103‑1115. (in Chinese) [百度学术]
郭伟娜, 张鹏, 鲍玖文, 等. 粉煤灰掺量对应变硬化水泥基复合材料力学性能及损伤特征的影响[J]. 建筑材料学报, 2022, 25(6):551‑557. [百度学术]
GUO Weina, ZHANG Peng, BAO Jiuwen, et al. Effect of fly ash content on mechanical properties and damage characteristics of strain‑hardening cementitious composites [J]. Journal of Building Materials, 2022, 25(6):551‑557. (in Chinese) [百度学术]
REDON C, LI V C, WU C, et al. Measuring and modifying interface properties of PVA fibers in ECC matrix [J]. Journal of Materials in Civil Engineering, 2001, 13(6):399‑406. [百度学术]
YU K Q, YU J T, DAI J G, et al. Corrigendum to “development of ultra‑high performance engineered cementitious composites using polyethylene (PE) fibers” [J]. Construction and Building Materials, 2019, 216:698. [百度学术]
LI Y Z, GUAN X C, ZHANG C C, et al. Development of high‑strength and high‑ductility ECC with saturated multiple cracking based on the flaw effect of coarse river sand [J]. Journal of Materials in Civil Engineering, 2020, 32(11):04020317. [百度学术]
HUANG B T, WU J Q, YU J, et al. Seawater sea‑sand engineered/strain‑hardening cementitious composites (ECC/SHCC):Assessment and modeling of crack characteristics [J]. Cement and Concrete Research, 2021, 140:106292. [百度学术]
朱彬荣, 潘金龙, 周震鑫, 等. 3D打印高延性水泥基复合材料的单轴受拉和受压行为[J]. 硅酸盐学报, 2021, 49(5):844‑854. [百度学术]
ZHU Binrong, PAN Jinlong, ZHOU Zhenxin, et al. Uniaxial tensile and compressive stress‑strain behavior of 3D printed engineered cementitious composites [J]. Journal of the Chinese Ceramic Society, 2021, 49(5):844‑854.(in Chinese) [百度学术]
KANDA T, LIN Z, LI V C. Tensile stress‑strain modeling of pseudo strain hardening cementitious composites [J]. Journal of Materials in Civil Engineering, 2000, 12(2):147‑156. [百度学术]
张聪, 夏超凡, 袁振, 等.混杂纤维增强应变硬化水泥基复合材料的拉伸本构关系[J]. 复合材料学报, 2020, 37(7):1754‑1762. [百度学术]
ZHANG Cong, XIA Chaofan, YUAN Zhen, et al. Tension constitutive relationship of hybrid fiber reinforced strain hardening cementitous composites [J]. Acta Materiae Compositae Sinica, 2020, 37(7):1754‑1762. (in Chinese) [百度学术]
LI V C. Performance driven design of fiber reinforced cementitious composites [C]//Proceedings of 4th RILEM International Symposium on Fiber. London:E&FN Spon, 1992: 12‑30. [百度学术]
姚淇耀, 陆宸宇, 彭林欣, 等. 氯盐侵蚀作用下BFRP筋增强海砂ECC的拉伸及弯曲性能试验[J]. 复合材料学报, 2022, 39(3):1215‑1227. [百度学术]
YAO Qiyao, LU Chenyu, PENG Linxin, et al. Experimental study on tensile and bending properties of sea sand ECC reinforced by BFRP bars under chloride salt erosion [J]. Acta Materiae Compositae Sinica, 2022, 39(3):1215‑1227.(in Chinese) [百度学术]
YAO Q Y, LI Z, LU C Y, et al. Development of engineered cementitious composites using sea sand and metakaolin [J]. Frontiers in Materials, 2021, 8:711872. [百度学术]
曹明莉, 许玲, 张聪. 高延性纤维增强水泥基复合材料的微观力学设计、性能及发展趋势[J]. 硅酸盐学报, 2015, 43(5):632‑642. [百度学术]
CAO Mingli, XU Ling, ZHANG Cong. Review on micromechanical design, performance and development tendency of engineered cementitious composite[J]. Journal of the Chinese Ceramic Society, 2015, 43(5):632‑642. (in Chinese) [百度学术]
王振波, 张君, 王庆. 混杂纤维增强延性水泥基复合材料力学性能与裂宽控制[J]. 建筑材料学报, 2018, 21(2):216‑221,227. [百度学术]
WANG Zhenbo, ZHANG Jun, WANG Qing. Mechanical behavior and crack width control of hybrid fiber reinforced ductile cementitious composites[J]. Journal of Building Materials, 2018, 21(2):216‑221, 227.(in Chinses). [百度学术]
LI V C, WU C, WANG S X, et al. Interface tailoring for strain‑hardening polyvinyl alcohol‑engineered cementitious composite (PVA‑ECC)[J]. ACI Materials Journal, 2002, 99(5):463‑472. [百度学术]
MAALEJ M, LI V C. Flexural/tensile strength ratio in engineered cementitious composites[J]. Journal of Materials in Civil Engineering, 1994, 6(4):513‑528. [百度学术]